Macau on the PotomacNational Harbor prepares for casino gambling.

Fireworks exploded over the Potomac River on election night, as the developers of National Harbor celebrated Maryland voters’ passage of Question 7, which expands the state’s gambling to include table games—and will allow MGM to build an $800 million casino in the Prince George’s County microcity to D.C.’s south. Or should that be the “special administrative district” to D.C.’s south? There were plenty of reasons to oppose the referendum—for starters, where there’s gambling, there’s more gambling addiction, and existing gaming in Maryland hasn’t benefited education as much as pols promised—but now that the MGM project is fait accompli, Washingtonians should be excited about getting their very own Macau. Just as that gambling mecca, a former Portuguese trading port, sits across the Zhujiang River Estuary from Hong Kong, will National Harbor be our 21st century den of sin down the Potomac? Consider this: You no longer have to drive to Charles Town or Atlantic City to shoot craps. When your luck goes cold you can page Uber and go home, content that all those societal ills are the problem of someone else’s jurisdiction.